Fiber-reinforced composite materials are widely adopted as a material that is lightweight and excellent in high physical properties because fragility of a matrix can be reinforced with fibers having high strength.
However, molded articles including only a synthetic resin or a metal can be molded easily and quickly by injection molding or press molding, whereas fiber-reinforced composite materials encountered such a problem that moldability in a short time or complicated moldability is poor due to the presence of reinforcing fibers with poor fluidity contained therein.
In particular, in the case of using a thermosetting resin for the matrix resin, in addition to the matter that it takes a time for integrating the matrix resin with fibers, a time for setting the matrix resin was needed. Then, though fiber-reinforced composite bodies using a thermoplastic resin in place of the conventional thermosetting resin have been attracting attention, there was encountered such a problem that in general, the resin viscosity during the process is high as compared with the thermosetting resin, and thus, it takes a more time for impregnating the fibers with the resin.
As a method for solving these problems, for example, in the thermoplastic stamping molding method, there is disclosed a method in which chopped fibers having been previously impregnated with a resin are put into a die, and the fibers and the resin are allowed to flow within the die, thereby obtaining a product shape (see Patent Document 1 and the like). However, since it is required to secure high fluidity within the die, there were encountered such problems that a thin-walled product cannot be made, and that control is difficult.
In addition, there is also proposed a technology of subjecting thermoplastic resin pellets including reinforcing fibers to injection molding (see Patent Document 2 and the like); however, there was encountered such a problem that the length of the pellet is an upper limit of the fiber length in the production, and that the reinforcing fibers are cut during the kneading process, and thus, a thorough reinforcing effect is not obtained.
Furthermore, all of the above-described both methods encountered such a problem that the fibers are apt to be oriented, and the reinforcing effect presents strongly only in one direction, and thus, an isotropic material is hardly obtained.
Then, Patent Document 3 discloses a production method of press molding a fiber matrix structure including reinforcing fibers and a thermoplastic resin, and specifically, a polyamide resin or the like is used as the matrix resin. However, in the case of using a usual resin as the matrix resin, for example, in the case of using an amorphous resin, there was encountered such a problem that the chemical resistance to an alkali, chlorine, or the like is poor. Meanwhile, in the case of using a crystalline resin, the general chemical resistance is enhanced; however, for example, in the case of using a polyamide resin, there were encountered such problems that the acid resistance is poor, and that the dimensional change to be caused due to water absorption is large.
(Patent Document 1) JP-A-11-81146
(Patent Document 2) JP-A-9-286036
(Patent Document 3) JP-A-2011-178890